The present invention relates to display color gamut mapping and image color enhancement.
The advance of flat panel display (FPD) technology is able to make the color gamut of a display wider than the sRGB/ITU-R BT.709 color gamut that is widely used by the current HDTV and Internet/computers standards. A color gamut mapping algorithm (GMA) maps RGB (red, blue, green) display values of a color in a color gamut to new RGB values in a new gamut. The RGB display values before and after a GMA usually are different, and may or may not represent the same physical color. The input of a GMA is also 3 dimensional and the output of a GMA is also 3 dimensional.
An image color enhancement algorithm maps color of an image to new more saturated colors. Image color enhancement is also a three dimensional mapping technique. The input of color enhancement is 3 dimensional and the output is 3 dimensional. Most existing current image color enhancement techniques typically boost saturation of colors. In the hue-saturation color wheel such as the one shown in FIG. 1, a typical color enhancement technique moves colors outward on the radial direction as shown by the arrows. A GMA from small gamut to big gamut also typically boosts saturation of colors. Therefore, a GMA from small gamut to big gamut and an image color enhancement algorithm have similar challenges.
By way of example, televisions have built-in color enhancement techniques to enhance unsaturated colors in certain content and let viewers set their color preferences. Because the human eye is very sensitive to the skin color, it is desirable for a color enhancement technique to render skin colors properly. It is also desirable for a color enhancement technique to separately adjust skin colors and non-skin colors using different characteristics.
Some GMA color enhancement techniques have the capability of protecting skin colors. These techniques are typically pixel-based. When the color of a pixel is mapped/enhanced to a new color, the conversion from the old color to the new color is fixed, and is not affected by other pixels. Because pixel-based color enhancement techniques with skin color protection cannot overcome the issue that the colors of skin and non-skin are highly overlapped, these techniques cannot effectively protect skin tones to maintain their calibration with the input image.